As the use of laparoscopic surgery has grown, the tools available for use in laparoscopy continue to increase and have become quite sophisticated. Considerable effort and skill have been applied to the development of instruments and devices that make laparoscopy safe, effective and economical.
The trocars used to perform laparoscopic surgery receive much attention. The trocar is generally understood to be an assembly including a cannula, a seal housing and an obturator. The cannula is typically an elongate tubular structure that is sized and configured to traverse a biological body wall and communicate between external a biological body to a body cavity within the biological body. Cannulas that are presently used for laparoscopic procedures typically range in size from about 3 mm to about 15 mm in diameter and from about 6 cm to about 18 cm in length. The seal housing may include an enlarged proximal portion of the cannula or may be a separate component that is coupled to the proximal end of the cannula. The seal housing contains at least one substantially gastight seal that allows instruments to be passed through the cannula and utilized in the surgical procedure while maintaining internal pressure, or pneumoperitoneum, of the body cavity into which the cannula communicates. The obturator is typically an elongate sharpened device that is sized and configured to penetrate the body wall. The obturator is often inserted into the lumen of the cannula so that the cannula may be inserted into the body wall concurrently with the obturator. With the distal end of the cannula positioned within the body cavity, the obturator may be removed from the cannula and the trocar is ready for use as a surgical port through which appropriate instruments are used.
Although trocars have been, and continue to be, the subject of much invention, trocars are much the same as they have always been. Seals have improved, materials have evolved and manufacturing methods have resulted in more economical trocars, but there are still unmet needs. What has been needed is a trocar that does not require a relatively large force to penetrate the body wall, such as the abdominal wall, of a patient. Also needed is a trocar that substantially eliminates bleeding at the trocar site during the laparoscopic procedure.
One response to the need for reduced trocar penetration force has been advanced by the device disclosed in U.S. Pat. No. 5,431,676 to Dubrul, et al. (Dubrul, et al. '676). The device of Dubrul, et al. '676 includes a woven tubular sheath that is placed through a puncture or small incision in the body wall. With the sheath placed across the body wall, a trocar is advanced through the sheath and into the body cavity. Although the device of Dubrul, et al. '676 reduces the penetration force required to advance the trocar through the body wall, the penetration force is not reduced significantly and the force required to dilate the tissue adjacent the sheath can be overwhelming. Use of the device of Dubrul, et al. '676 requires the user to force a cannula and a blunt obturator through a collapsed, reinforced sheath that is confined circumferentially over its entire tissue-contacting length. In a muscular patient, this constrictive force can be significant. It is not uncommon for the force required to overcome the resistance to penetration to exceed eighteen (18) kilograms, even though in some cases a force of four and one-half (4.5) kilograms may be considered excessive.